Also in Hesychius (alpha6711) and other lexica.
The headword, a sigmatic aorist middle infinitive, and its gloss, a strong aorist active infinitive, are given in LSJ (web address 1) under a)potugxa/nw "fail to succeed, miss the goal" as alternative forms. There was confusion in ancient and modern times over the relationship between the simple verbs teu/xw 'work at or create something as a craftsman' (web address 2) and tugxa/nw 'happen' (web address 3). It was thought that the latter borrowed its future middle forms from the former, and hence also this aorist middle. Modern scholars have, however, shown that both come from an underlying root for hitting or working with a tool, with aim or with planning, but have different semantic histories, especially in the compounds; see references below. A.W. Gomme in his Commentary on Thucydides points out that the historian uses the aorist of tugxa/nw not to mean "happened, was lucky" but "succeeded in a tactical goal (with a bit of luck)". Dyer (below) 660 attributes the verb's semantic history to shooting and hitting a target as in archery (cf. alpha 1493, alpha 3076, alpha 3159, alpha 3573, pi 1687) and points to this sense at Homer, Iliad 5.287 (eta 286), 582, 23.857. For other compounds see alpha 4399, epsilon 1468, epsilon 1469, epsilon 2674, epsilon 3781, pi 1321, sigma 1638, sigma 1639.